title: Femtosecond double-pulse fabrication of hierarchical nanostructures based on electron dynamics control for high surface-enhanced Raman scattering.
abstract: This Letter presents a simple, efficient approach for high surface-enhanced Raman scattering by one-step controllable fabrication of hierarchical structures (nanoparticles+subwavelength ripples) on silicon substrates in silver nitrate solutions using femtosecond double pulses based on nanoscale electron dynamics control. As the delays of the double pulses increase from 0 fs to 1 ps, the hierarchical structures can be controlled with (1) nanoparticles--the number of nanoparticles in the range of 40-100 nm reaches the maximum at 800 fs and (2) ripples--the subwavelength ripples become intermittent with decreased ablation depths. The redistributed nanoparticles and the modified ripple structures contribute to the maximum enhancement factor of 2.2×10(8) (measured by 10(-6)  M rhodamine 6G solution) at the pulse delay of 800 fs.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Lan
authors.initials: L
authors.lastname: Jiang
authors.forename: Xuesong
authors.initials: X
authors.lastname: Shi
authors.forename: Cong
authors.initials: C
authors.lastname: Li
authors.forename: Yongfeng
authors.initials: Y
authors.lastname: Lu